This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Emerging evidence has linked mutations in myofiliment proteins to the development of genetic cardiomyopathies and myocardial dysfunction. Troponin C is the protein responsible for the transmission of the calcium-binding signal and triggering the contractile cycle. Dr. Liao and her associates identified two novel missense mutations in human cardiac troponin C at amino acid residues 59 (E59D) and 75 (D75Y) from a patient with idiopathic dialated cardiomyopathy, the first identified mutation of troponin C from any human disease. These missense mutations are located within the calcium-binding domain that regulates myocardial contraction, and result in decreased myofilament calcium responsiveness. These results showed mutations in troponin C contribute to the decreased contractile function in the diseased human heart. To determine the structure-function relationship, they designed a number of troponin C mutants based on replacing specific amino acid residues located within regulatory calcium-binding domains. We used in-gel proteolytic digestion, followed by MALDI-TOF and tandem mass spectrometry to structurally verify specific mutations. Additionally, semiquantitation of synthetic mutant peptides enabled estimation of relative expression levels. This mutational model system is helping to define how mutations in cardiac troponin C alter calcium responsiveness in cardiac myofilaments and, consequently, determine myocardial contractility. The paper describing these results was featured on the cover of Biophys. J. in May 2008.